御中
おんちゅう · onchuu · JLPT N2 · noun
Messrs.
御 (honorable) + 中 (inside) = sent 'to the inside' of an organization, so 'Messrs.' goes on group mail
御中 is used for organizations, not individuals. 御 means honorable and 中 means middle or inside, so the letter goes to the group inside the company. Use 様 for named people.
中 — vertical stroke 丨 through enclosure 口
Pictograph of a banner or pole piercing the center of a target or territory, depicting the idea of 'middle' or 'center'. The horizontal frame represents boundaries, and the vertical line marks the central axis. The meaning extended from spatial center to 'middle, central, China' (中国, the Middle Kingdom).